A leading theory about Alzheimer's Disease (AD) suggests that toxic plaques of beta-amyloid protein accumulate in the aging brain, destroy neurons, and cause declining cognitive function. This theory has been deeply scrutinized and modified over the past two decades of intensive research.

The notable, but poorly understood role of amyloid has driven both treatment strategies and diagnostic strategies for Alzheimer's Disease. In fact, a great majority of efforts to treat Alzheimer's disease have been based on agents that either slow production of amyloid, alter the form of amyloid, or remove amyloid from the brain. Likewise, many diagnostic approaches have been driven by measures of the amount of amyloid in the brain or spinal fluid.

New research from the Penn Medicine Department of Radiology, published in the Neurobiology of Aging, suggests that the location of amyloid plaques in the brain may be more important that the amount of amyloid in the brain. In fact, it has been widely observed (but as yet unexplained) that many older adults, who died with complete cognitive integrity, were shown at autopsy to have massive amounts of amyloid plaques in their brains. Evidence favoring amyloid location over amyloid burden in diagnosing Alzheimer's disease offers a potential explanation for these puzzling observations.

The amyloid hypothesis has evolved considerably since it was first introduced. This research may offer a further refinement and a better understanding of the complex pathology of Alzheimer's Disease.

Historically, science has tried to answer this question by measuring the duration of concussion symptoms. Often, depending on the severity of the concussing event, symptom such as dizziness, blurred vision, and interrupted sleep are completely resolved within a few days or a couple of weeks.

However, we also know that many injuries, to various tissues in the body, are not completely healed until long after clinical symptoms have faded. This may also be true of injuries to the brain.

In fact, new research from the Mind Research Network in Albuquerque, N.M. supports such thinking. In a paper published in the online edition of Neurology, researchers showed that physical changes to concussed brains persisted for many months after symptoms had resolved.

One implication is that the brain needs longer to heal than the period demarcated by clear symptoms.

A second, and perhaps more important implication, is that brain injury and symptoms of brain injury may not be always correlated. In that regard, the constant, low-impact collisions of many sports may be injuring the brain in ways that are not obvious in terms of symptoms, but are injurious just the same.